The goal of this study was to revise the development length equation of ACI 318- 05 and to better reflect test results for high-strength concrete. The revision of the equation was accomplished using test results tabulated in the Database 10-2001maintained by ACI committee 408. Equations for development length in ACI 318-05 and ACI 408.3 examined to understand the issues to be considered for revision on the variability of test data. The development length equation in ACI 318-05 was very conservative for [compressive strength of concrete][less than or equal to]14,000 psi based on the experimental data in Database 10-2001 of ACI Committee 408. On the contrary, the ACI 318-05 may be less conservative for high-strength concrete, [compressive strength of concrete] [greater than or equal to]14,000 psi . Thus, modified design equations were proposed to provide realistic values for normal strength concrete and conservatively for high-strength concrete. The ACI 318-05 equation was modified for 1) compressive strength of concrete and 2) confinement as expressed by the term [minimum side cover, cover over the bar or wire, or one-half the center-to-center spacing of the bars or wires] + [contribution of confining reinforcement across potential splitting planes] / [normal diameter of bar] in ACI 318-05. The basic assumption is that bar stress is a linear function of development length, and development length is the length required for bar stresses to reach the yield. / text

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Early and accurate prediction of the compressive strength of concrete is important in the construction industry. Modeling the compressive strength of concrete to obtain a balance and equality between prediction accuracy, time and uncertainty of the prediction is a very difficult task due to the highly nonlinear nature of concrete. For structural engineering purposes, the 28- day compressive strength is the most relevant parameter. In this study, an attempt has been made to predict the 28-day compressive strength of concrete using Relevance Vector Machine (RVM). An RVM belongs to the class of sparse kernel classifiers, which are powerful tools in classification and regression. It has a model of identical functional form to the popular and state-of-the-art `Support Vector Machine (SVM)'. The benefits of using RVM include automatic estimation of nuisance parameters, probabilistic prediction and the ability to model complex data with little information. A total of 425 different data of high performance mix designs were collected from the University of California, Irvine repository. The data used to predict the compressive strength consisted of nine components. The RVM model was trained and tested using 395 and 30 data sets respectively. The model's performance was assessed at the end of the training and testing period using four performance measures; coefficient of determination, root-mean-square error, percentage of relevance vectors and residual plots. All the performance measures confirmed the accuracy of the model. The results of the study suggested that RVM is an effective tool for predicting the 28- day compressive strength of concrete from its mix ingredients.

Made available in DSpace on 2015-08-20T17:09:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-06-27. Added 1 bitstream(s) on 2015-08-20T17:27:08Z : No. of bitstreams: 1 000844276.pdf: 29036188 bytes, checksum: 616a25863a975b7bbef55bbbb94efb03 (MD5) / O concreto celular, que se caracteriza por ter um peso próprio reduzido pela incorporação artificial de ar no concreto, pode constituir uma alternativa ao concreto armado nas estruturas de pequeno e médio porte. A baixa solicitação dos elementos estruturais permite aproveitar as principais vantagens do material: melhoria da isolação, economia de material para produzir o concreto e facilidade do transporte dos elementos pré-moldados. A fim de conhecer melhor o desempenho mecânico do material para aplicações estruturais, o presente trabalho trata da avaliação da aderência entre o concreto celular e as barras de aço. Para estudar esse fenômeno, foram realizados ensaios de arrancamento com barras de diâmetro igual a 4,2 mm, parcialmente imersas em corpos-de-prova de concreto cilíndrico. A variação da massa específica do concreto e a presença ou não de uma barra transversal dentro do cilindro constituem as variáveis da pesquisa. No total foram realizados três tipos de concreto, com massa específica aparente aos 28 dias de 2255, 1565 e 1510 kg/m 3 . Entre outros resultados, a pesquisa revelou, pelo arrancamento de barras simples de diâmetro igual a 4,2 mm, o forte decréscimo da tensão de aderência junto com o rebaixamento da massa específica aparente do concreto. Confrontando os resultados com trabalhos semelhantes, a elevada relação água/cimento parece ser o parâmetro que mais influenciou os resultados. Também, parâmetros que podem ter influenciado a tensão de aderência são a quantidade de agente espumígeno colocada nos concretos, a utilização de agregado graúdo e talvez o diâmetro das barras arrancadas. A introdução da barra transversal no meio do cilindro permitiu obter um ganho de resistência ao arrancamento da barra longitudinal, que cresceu junto com o rebaixamento da massa específica do concreto celular. Assim, a utilização de ancoragens especiais (não exclusivamente retas), que permite... / Cellular concrete is a lightweight concrete obtained by aerating agent, which produces air-voids into the mixture. Low loads acting on houses or small buildings permits to use cellular concrete advantages: good thermal insulation, lower concrete production costs and simplification of precast transportation. To improve the mechanical characteristic of structural cellular concrete knowledge, this work deals with bond between cellular concrete and steel rebars. Pull-out tests of 4,2 mm diameter rebars partly immersed into concrete cylinders were made. Concrete unit weight variation and setting of a transverse rebar into the concrete cylinder center constitute the variables of the work. Three types of mixture were prepared: one without aerating agent (with a dry unit weight of 2255 kg/m 3 ), and two with different aerating agent rates (with a dry unit weight equal to 1565 and 1510 kg/m 3 ). One of the conclusions of the study is the large decrease of bond stress between 4,2 diameter rebars and cellular concrete, due to concrete unit weight reduction. Comparison of results with others studies reveals that water/cement ratio could be the main variable which influences bond stress. Moreover, other variables like aerating agent quantity introduced into the mixture, coarse aggregate use or rebar diameter could influence the bond stress value. Transverse rebar introduced into concrete cylinder center increased the ultimate pull-out force of the test: the gain of bond produced by the transverse rebar grew up when the cellular concrete unit weight had been reduced. Therefore, special anchorages (not exclusively straight), permitting bond improvement between cellular concrete and 4,2 mm diameter rebar could be a solution to improve the mechanical performance of cellular concrete

Orientador: Jefferson Sidney Camacho / Co-orientador: Guilherme Aris Parsekian / Banca: Mauro Mitsuuchi Tashima / Banca: Gilberto Carbonari / Resumo: O concreto celular, que se caracteriza por ter um peso próprio reduzido pela incorporação artificial de ar no concreto, pode constituir uma alternativa ao concreto armado nas estruturas de pequeno e médio porte. A baixa solicitação dos elementos estruturais permite aproveitar as principais vantagens do material: melhoria da isolação, economia de material para produzir o concreto e facilidade do transporte dos elementos pré-moldados. A fim de conhecer melhor o desempenho mecânico do material para aplicações estruturais, o presente trabalho trata da avaliação da aderência entre o concreto celular e as barras de aço. Para estudar esse fenômeno, foram realizados ensaios de arrancamento com barras de diâmetro igual a 4,2 mm, parcialmente imersas em corpos-de-prova de concreto cilíndrico. A variação da massa específica do concreto e a presença ou não de uma barra transversal dentro do cilindro constituem as variáveis da pesquisa. No total foram realizados três tipos de concreto, com massa específica aparente aos 28 dias de 2255, 1565 e 1510 kg/m 3 . Entre outros resultados, a pesquisa revelou, pelo arrancamento de barras simples de diâmetro igual a 4,2 mm, o forte decréscimo da tensão de aderência junto com o rebaixamento da massa específica aparente do concreto. Confrontando os resultados com trabalhos semelhantes, a elevada relação água/cimento parece ser o parâmetro que mais influenciou os resultados. Também, parâmetros que podem ter influenciado a tensão de aderência são a quantidade de agente espumígeno colocada nos concretos, a utilização de agregado graúdo e talvez o diâmetro das barras arrancadas. A introdução da barra transversal no meio do cilindro permitiu obter um ganho de resistência ao arrancamento da barra longitudinal, que cresceu junto com o rebaixamento da massa específica do concreto celular. Assim, a utilização de ancoragens especiais (não exclusivamente retas), que permite... / Abstract: Cellular concrete is a lightweight concrete obtained by aerating agent, which produces air-voids into the mixture. Low loads acting on houses or small buildings permits to use cellular concrete advantages: good thermal insulation, lower concrete production costs and simplification of precast transportation. To improve the mechanical characteristic of structural cellular concrete knowledge, this work deals with bond between cellular concrete and steel rebars. Pull-out tests of 4,2 mm diameter rebars partly immersed into concrete cylinders were made. Concrete unit weight variation and setting of a transverse rebar into the concrete cylinder center constitute the variables of the work. Three types of mixture were prepared: one without aerating agent (with a dry unit weight of 2255 kg/m 3 ), and two with different aerating agent rates (with a dry unit weight equal to 1565 and 1510 kg/m 3 ). One of the conclusions of the study is the large decrease of bond stress between 4,2 diameter rebars and cellular concrete, due to concrete unit weight reduction. Comparison of results with others studies reveals that water/cement ratio could be the main variable which influences bond stress. Moreover, other variables like aerating agent quantity introduced into the mixture, coarse aggregate use or rebar diameter could influence the bond stress value. Transverse rebar introduced into concrete cylinder center increased the ultimate pull-out force of the test: the gain of bond produced by the transverse rebar grew up when the cellular concrete unit weight had been reduced. Therefore, special anchorages (not exclusively straight), permitting bond improvement between cellular concrete and 4,2 mm diameter rebar could be a solution to improve the mechanical performance of cellular concrete / Mestre

Este estudo objetivou avaliar a resistência máxima às forças de compressão entre dois grupos diferentes de coroas em porcelanas livres de metal cimentadas sobre dentes naturais e um grupo formado por dentes caninos naturais hígidos e comparar os resultados obtidos com os de (Chaves, 2001), em seu trabalho de Doutorado onde também se avaliou a resistência máxima às forças de compressão entre coroa metalo cerâmica fraturada e reparada com resina composta com coroa metalo cerâmica integra e dente natural permanente. No presente estudo foram feitos vinte preparos para coroa total em dentes naturais caninos e divididos em dois grupos para confecção de dez coroas do sistema cerâmico aluminizado infiltrado por vidro (Angelus Brasil) e dez coroas em porcelana feldspática Noritake ® (Noritake Kisai CO. Cada grupo de coroas foi cimentado com cimento resinoso auto adesivo RelyX Unicem ® , (3M ESPE, Brasil) com o objetivo de aumentar a resistência da porcelana frente às forças de compressão. O teste de compressão foi realizado em uma máquina de ensaio universal KRATOS, através de uma carga aplicada axialmente no ápice da borda incisal de cada espécime até a fratura. Os dados foram submetidos à análise de Variância ANOVA (p < 0,05) e teste de Tukey para comparação entre grupos. Os resultados mostraram que não houve diferença estatisticamente significante entre a coroa de porcelana aluminizada infiltrada por vidro e o dente natural. A coroa de porcelana feldspática apresentou-se menos resistente com relação ao dente natural e coroa de porcelana aluminizada infiltrada por vidro. / The objective of this study is evaluate the maximum load resistance between two different groups of porcelain metal free crown seated on natural teeth and a group of natural canine and to compare the results gotten with the ones of (Chaves, 2001), in its work of Doutorado where also the ultimate strength to the forces of compression between metalo ceramic broken and repaired with composite resin with ceramic crown metaloceramic integrates and permanent natural tooth. In the present study twenty natural canine teeth were prepared for crown canines and divided in two groups: aluminized porcelain crown infiltrated for glass (Angelus Brazil) and feldspathic Noritake Kisai Noritake (co). Crowns were seated using self adhesive resin cement RelyX Unicem (3M ESPE, Brazil) Compression testing was performed by a universal testing machine (KRATOS) by a load applied axially in incisal of each specimen until occurs the fracture. The data were analyzed by one way analyses of variance (ANOVA) and Tukey test for comparison between groups. The results showed that it did not have statistical significant difference between aluminized porcelain crown infiltrated by glass and natural tooth. The feldspathic porcelain crown presented less resistant than natural tooth and aluminized porcelain crown infiltrated by glass. .

The variation in the compressive strength of concrete block masonry was studied at elevated temperatures. Small specimens known as wallettes were used to obtain the compressive strength under steady state conditions. Eighteen wallettes were made of lightweight concrete blocks and 1:1:5 mortar proportion. The target temperatures were 20°C, 200°C, 400°C, 600°C, 700°C and 800°C. Initially load-deflection relationships were determined from the experimental wallettes and later they were converted into stress-strain relationships. Although the goal was to determine the compressive strength, other parameters were also studied such as modulus of elasticity, temperature-time relationships, modes of failure, material degradation, and change of colour.Lightweight concrete blocks were also tested to determine the compressive strength at equal temperatures applied for the wallettes. The blocks belonged to the same batch used for the wallettes. The tensile behaviour of mortar was determined at 20°C, 200°C and 400°C.Once the mechanical properties of the masonry wallettes, units and mortar were determined, they were used as input data to develop finite element models to simulate the same behaviour of the experimental wallettes. Finally, using the experimental and numerical results from the wallettes, they were used to predict the behaviour of 3m height walls.

Increasing use of rock materials like shale in building, roofing, embankment filling, brick manufacturing, and in other civil structure application makes it an important rock to consider in construction engineering. Knowledge of thermal and physical properties of shale as building material is required to predict the rock's strength and permanence against weathering. Inconsistent heat capacity of anisotropic rock can result in differential heat flow. This tendency can expand the building materials leading to reduction in strength and initiate disintegration. Authors have studied various thermo-physical properties of anisotropic shale from Tennessee, which is commonly used as building stones and bricks. Experiment was designed to measure the basic thermal property, 'heat capacity' of shale. Series of laboratory tests including durability, strength, specific gravity, moisture content, and porosity were conducted to determine the physical and mechanical behavior of the samples. Results indicated that properties like porosity, strength and heat capacity varied significantly within samples, where as specific gravity and moisture content yielded steady values. Multivariate regression analysis was performed to evaluate possible correlations among the tested properties. Strong positive relationship was evident between heat capacity, and porosity. Heat capacity and Unconfined Compressive Strength of shale were inversely related. This study emphasized that physical and thermal properties of shale are directly linked with strength and durability of the rock mass.

Adobe is a building material that has been used since ancient times, but is not as widely used as clay bricks or concrete for housing construction. In addition, it uses a construction technique that has been passed down and improved from generation to generation. In view of this, the present work aims to improve the properties of adobe by using PET bottle fibers in its composition. A mechanical test and two physical tests were carried out for adobe with 0% (standard adobe), 2%, 4% and 6% PET fibers, where it was observed that the adobe with 6% PET fibers obtained the best results, since it increased the compressive strength of the adobe by 19%, reduced the absorption percentage by 12% and finally reduced the density by 16.4%. Therefore, the addition of PET fibers in adobe is recommended, as it contributes to improve its mechanical and physical properties. Additionally, it reduces pollution in streets, rivers, parks, etc. because it promotes the recycling of PET bottles.

Soil cement has been used as a means of stabilizing highway pavement layers, airport pavement layers, embankments, and foundations for decades. The technology uses a compacted mixture of soil, cement, and water to form a hardened material layer that has specific strength and durability properties. Even after decades of utilization, however, design of soil cement pavement layers has room for enhancement. This thesis investigates factors that influence the design and performance of cement stabilized pavement layers in Mississippi. A survey was conducted to collect information about soil cement design procedures from across the U.S. The factors examined in the laboratory investigation are strength gain with time, unconfined compressive strength variability, elastic modulus, and wheel tracking. More than 1,100 specimens were tested to determine the influence of these factors on the design and performance of soil cement pavement layers.